A systematic review of meta-analyses

Background: The efficacy and safety of hypnotic techniques in somatic medicine, known as medical hypnosis, have not been supported to date by adequate scientific evidence.

Methods: We systematically reviewed meta-analyses of randomized controlled trials (RCTs) of medical hypnosis. Relevant publications (January 2005 to June 2015) were sought in the Cochrane databases CDSR and DARE, and in PubMed. Meta-analyses involving at least 400 patients were included in the present analysis. Their methodological quality was assessed with AMSTAR (A Measurement Tool to Assess Systematic Reviews). An additional search was carried out in the CENTRAL and PubMed databases for RCTs of waking suggestion (therapeutic suggestion without formal trance induction) in somatic medicine.

Results: Out of the 391 publications retrieved, five were reports of meta-analyses that met our inclusion criteria. One of these meta-analyses was of high methodological quality; three were of moderate quality, and one was of poor quality. Hypnosis was superior to controls with respect to the reduction of pain and emotional stress during medical interventions (34 RCTs, 2597 patients) as well as the reduction of irritable bowel symptoms (8 RCTs, 464 patients). Two meta-analyses revealed no differences between hypnosis and control treatment with respect to the side effects and safety of treatment. The effect size of hypnosis on emotional stress during medical interventions was low in one meta-analysis, moderate in one, and high in one. The effect size on pain during medical interventions was low. Five RCTs indicated that waking suggestion is effective in medical procedures.

Conclusion: Medical hypnosis is a safe and effective complementary technique for use in medical procedures and in the treatment of irritable bowel syndrome. Waking suggestions can be a component of effective doctor–patient communication in routine clinical situations.

Hypnosis for purposes of medical treatment goes back a long way. The British Medical Association endorsed the use of hypnosis in somatic medicine in 1955, on the basis of case reports and series backed up by expert consensus, and the American Medical Association followed suit in 1958 (1, 2). Whether robust evidence exists for the efficacy and safety of hypnosis in somatic medicine in the era of evidence-based medicine (EBM) (3) remains to be clarified. Because systematic reviews with quantitative analysis (meta-analyses) of randomized controlled trials provide the highest level of evidence in EBM (3), we decided to carry out a systematic review of meta-analyses on medical hypnosis.

The aims of this article are as follows:

To define the various forms of hypnosis

To describe the requirements that have to be fulfilled before therapeutic hypnosis can be carried out

To provide a historical overview of the use of hypnosis in medicine and the assessment of its efficacy

To identify the indications for medical hypnosis supported by robust evidence

To present the evidence for use of positive suggestions as a component of effective doctor– patient communication.

Definitions

The term “hypnosis” is used to mean both an altered state of consciousness (synonym: hypnotic trance) and the procedure by which this state is induced (4). During a hypnotic trance physiological, cognitive, and affective processes as well as behavior can be modified. A hypnotic state and hypnotic phenomena can be induced by another person (therapist) or alone (self-hypnosis). The subjective experience of hypnosis is characterized by a high degree of authenticity (experienced as real) and involuntariness (“it happens by itself”) (4).

Hypnosis can be distinguished from other states of consciousness such as normal wakefulness, sleep, deep relaxation, or meditation by means of electroencephalography (EEG) and imaging modalities (4). A hypnotic trance is characterized by a number of physiological and mental reactions, e.g., altered perception of time, selective amnesia, regression to a younger age (retrieval of memories or experiences from an earlier developmental stage), a marked inward focus, and heightened suggestibility, i.e., a stronger reaction to suggestions (4). In clinical situations associated with high affective participation of the patient, such as emergencies, diagnostic and therapeutic interventions, or communication of a serious diagnosis, hypnotic phenomena may occur spontaneously (e1, e2).

Suggestions work via verbal and nonverbal signals that correspond to internal expectations and have a powerful effect on mental and involuntary somatic processes. For example, cutaneous perfusion or the flow of saliva is not amenable to influence by a deliberate intellectual action, but can be affected by a suggestion, e.g., a picture or a story. In general use the word “suggestion” tends to imply manipulation, but in hypnosis it should be understood as meaning a proposal, an offer of options (“I suggest”). In contrast to the widespread preconceptions, hypnosis is not authoritarian, passive, and centered around the therapist, but a resource- and solution-oriented method in which the focus is on the patient's own potentials (4).

Applications of hypnosis

Depending on the goals, various applications of hypnotic techniques can be distinguished (4):

Medical hypnosis

– Alleviation of somatic symptoms

– Reduction of mental stress during medical treatment

– Amelioration of disordered physiological/biochemical parameters

– Facilitation of physiological/biochemical healing processes

Hypnotic communication

– Waking suggestions (suggestions without trance induction)

– Suggestions with the patient under general anesthesia

– Use of findings from hypnotherapy for effective doctor–patient communication

Hypnotherapy (psychotherapy with the patient in a trance)

– Improvement of problem management by giving the patient access to their own resources

– Basic research on somatic sensations (e.g., pain), emotions, and states of consciousness

Stage hypnosis

– Demonstration of hypnotic phenomena to entertain an audience

The perception of hypnosis as an authoritarian, manipulative technique, nourished particularly by its use in stage shows, represents the greatest barrier to the (re)integration of hypnosis into medical treatment.

Phases of medical hypnosis

A session of medical hypnosis generally lasts between 20 and 50 min and can be divided into various phases (4):

Verification of the indication; explanation (correction of inappropriate anxiety or false expectations); definition of goal(s)

In Israel and Sweden, hypnosis may be carried out only by physicians and psychologists who have received appropriate training. In Germany, from the legal point of view, anyone can offer hypnosis for non-medical reasons. Treatment of illness by means of hypnosis requires a license to perform procedures for the purpose of healing (medical and psychological psychotherapists, child and adolescent psychotherapists, naturopaths) (e3). Medical hypnosis can be carried out by physicians of all patient-related specialties in the framework of basic psychosomatic care. An invoice for relaxation hypnosis according to the official German schedules for physicians’ fees (Uniform Value Scale, Einheitlicher Bewertungsmaßstab) can be submitted only by persons who possess a qualification in basic psychosomatic care and have successfully completed a course in hypnosis comprising two units of 16 hours each (e4). Most medical and psychological psychotherapists and child and adolescent psychotherapists learn the techniques of hypnotherapy as a supplementary qualification. As a rule hypnotherapists are also trained in other methods of psychotherapy.

Details of the history of hypnosis and assessment of its efficacy prior to the introduction of evidence-based medicine (EBM) are provided in eBox 2.

eBox 2

The history of hypnosis and assessment of its
efficacy before the advent of evidence-based
medicine (EBM)

This review was conducted according to the recommendations of the Cochrane Collaboration for systematic reviews of previously published reviews and the recommendations of the Joanna Briggs Institute for umbrella reviews (6).

Systematic survey of the literature

The Cochrane databases CDSR and DARE and PubMed were searched for systematic reviews (SRs) published in the period January 2005 to June 2015. The following search terms were used: “review,” “meta-analysis,” and “hypnosis”. We searched PubMed with “((“hypnosis”[MeSH] OR “hypnosis, dental”[MeSH]) AND (“meta-Analysis” [Publication Type] OR “review” [Publication Type])) OR ((hypnosis OR hypnotherap*) AND (meta-analy* OR metaanaly*))”. Moreover, the reference lists of the SRs identified were inspected for further SRs. With regard to waking suggestions we searched the databases Central and PubMed for randomized controlled trials (RCTs) using the terms “suggestion” [MeSH] and “hypnotic suggestion”. Finally, for all topics we asked experts in medical hypnosis about SRs.

Inclusion criteria

The following conditions regarding study type, indications, setting, and study population had to be fulfilled:

Study type: We included SRs with meta-analysis of (quasi-)RCTs on hypnosis as intervention for somatic medical indications. In the event of serial publications by the same group of authors we used the most recent publication. We selected inclusion of at least 400 patients in quantitative analysis (meta-analysis) of the study results as a quantitative criterion of robust evidence (7).

Indications: The endpoints of the meta-analysis had to be somatic symptoms (e.g., pain or nausea) or physiological findings (e.g., bleeding time or airway resistance) and/or mental stress during medical treatments and/or cost-related data (e.g., operating time, legth of hospital stay, or drug consumption). We excluded meta-analyses of RCTs on psychiatric and psychotherapeutic indications (e.g., anxiety disorders, depressive disorders, addiction/abuse, or behavioral disorders) and meta-analyses of RCTs on various diseases (e.g., psychosomatic illnesses) in which no subgroup analyses were conducted for individual diseases.

Setting and study population: No restrictions were imposed with regard to setting, age, or country.

Methodological quality

The methodological quality of the meta-analyses was verified using AMSTAR (A Measurement Tool to Assess Systematic Reviews) (8). AMSTAR scores of 0–4 were classified as low, 5–8 as intermediate, and 9–11 as high methodological quality (9).

Data extraction

The following characteristics of the meta-analyses were extracted independently by two of the authors (WH, MH) and discrepancies were resolved by consensus:

The medical indication

The number of RCTs/patients included

The age and sex of the patients

The type and duration of hypnosis

The nature of the control group

The instrument for and results of measurement of methodological quality of the included RCTs

The databases searched and the period covered

The findings regarding efficacy, tolerance, and safety

The authors' conclusions

The AMSTAR rating.

Given the heterogeneity of diseases and outcome variables, no quantitative data synthesis was planned from the outset.

Results: survey and inclusion

The database survey and the hand search identified 391 publications in total. Seventy-seven full texts were examined in detail (Figure). Fourteen meta-analyses (on topics such as chemotherapy-induced nausea and vomiting, fibromyalgia syndrome, and temporomandibular disorder) were excluded from analysis because they included fewer than 400 patients in their calculations (eTable 1) (e11–e24). Five meta-analyses were included in our qualitative review (10–14). The methodological quality was high in one meta-analysis, intermediate in three, and low in one (eTable 2). The characteristics of the original articles investigated in these five meta-analyses are outlined in Table 1.

Hypnosis was superior to standard treatment or attention control (controls) in reduction of emotional stress, (10, 13, 14), pain (10, 14), duration of convalescence, and drug consumption (10) in interventional procedures and operations. The effect size on emotional stress varied: it was slight in one meta-analysis (10), intermediate in another (14), and high in a third (13). The effect size on pain reduction was low (10, 14). The effect sizes of hypnosis in medical interventions were dependent on the methodological quality of the original studies (10, 14).

Gut-directed hypnosis was superior to the treatments used in the control groups with regard to the number of patients with an appropriate reduction of symptoms at the end of treatment (number needed to treat [NNT] 5) and at follow-up 6 months later (NNT 3) (12). Hypnosis was not more effective than standard treatment or attention control for pain during labor and childbirth (11).

Evaluation of the data on safety of hypnosis in two meta-analyses (pain during labor and childbirth, irritable bowel syndrome) (11, 12) revealed no signs of a higher rate of adverse effects than in controls (Table 2).

Table 2

Results of the meta-analyses of randomized controlled trials on medical hypnosis*

Anesthesia and surgery: The use of hypnosis instead of local anesthesia in dental surgery (e25) and in place of anesthesia for more extensive surgery (cholecystectomy, aortocoronary bypass operation) has been described in case reports (e26). However, hypnosis is being routinely used as a complement rather than an alternative to modern, safe techniques of anesthesia, primarily to minimize anxiety and stress. Hypnosis has been shown to reduce pain, anxiety, and the consumption of analgesics and sedatives to a statistically significant extent in patients undergoing operations under local or regional anesthesia (e27, e28).

An example of the efficacy of hypnotic communication—even without formal trance induction—is its application in waking craniotomies, as performed for instance for removal of a brain tumor close to the speech area or for deep brain stimulation. In these procedures the patient receives regional anesthesia of the head and remains awake for the whole duration of the brain surgery for purposes of neurological testing, with no need for sedation and additional analgesia. Dissociation to an inner place of tranquility away from the operating room plays an important part, as does the reinterpretation of sensory perceptions (e29).

Some German hospitals offer live or audio file–aided hypnosis as a complement to general and regional anesthesia.

Gastroenterology: With the aid of hypnosis—e.g., self-hypnosis or hypnosis by means of audio files— diagnostic esophagogastroduodenoscopy procedures can be carried out without sedation (e30). The use of audio files is also efficacious in irritable bowel syndrome (e31). These files can be given to patients with irritable bowel syndrome by their primary care physician or internist, and the progress with regard to symptom control can be discussed with the patients in the framework of basic psychosomatic care (e32). This aproach can greatly facilitate the clinical application of hypnosis. Gastroenterology departments in Great Britain (e33), Austria (e34), and the USA (e35) have integrated psychosocial services that offer live and audio file–aided hypnosis to patients with functional gastrointestinal disorders who do not respond well to conventional medicinal treatment (see eBox 1 for more on gut-directed hypnosis). Some office-based gastroenterologists in Germany offer hypnosis as an alternative to sedation in esophagogastroduodenoscopy.

Dentistry: The German Dental Hypnosis Society (Deutsche Gesellschaft für Zahnärztliche Hypnose) has trained around 3000 dentists in hypnosis. The society's website lists over 600 dentists who offer this service to their patients. The indications for which hypnosis is available are pronounced fear of dental treatment, gag reflex, intolerance of local anesthetics, and craniomandibular dysfunction. Hypnosis in the following forms is offered (e25):

The use of CDs developed specially for dental treatment (e.g. “Beim Zahnarzt ohne Spritze [Dental surgery without injection]”). At the beginning of the treatment session track 1 is played repeatedly over headphones, and at the end of treatment the patient is woken by track 2.

Delegation of the hypnosis to a trained member of staff (hypnosis assistant). In this case the dentist must also be trained in hypnosis, because he/she is responsible for the patient's welfare and must be able to deal with the rare cases of adverse reaction to hypnosis.

Induction of hypnosis by the dentist him-/herself. This takes 2 to 5 min for relaxation prior to an injection, about 10 min for treatment without local anesthesia.

It is advantageous to combine nitrous oxide and hypnosis, because the gas has an anxiolytic effect and increases suggestibility.

Some dentists who concentrate on treatment of patients with anxiety or craniomandibular dysfunction draw on the services of an external hypnotist.

Live hypnosis versus audio file–aided hypnosis

A meta-analysis of hypnosis in medical interventions demonstrated no significant differences in efficacy between live hypnosis and suggestion by means of audio files (14). Another meta-analysis by a different group of authors concluded that only live hypnosis, which is more apt to provide the context of a personal relationship, significantly reduced postoperative anxiety and pain. Both live and audio file–aided hypnosis significantly decreased postoperative nausea and consumption of analgesics (10).

Waking suggestions in doctor–patient communication

The German Medical Assembly 2015 spoke out in favor of strengthening physicians’ communicative competence (15). In our opinion, together with authentic and empathetic interaction (16), effective doctor–patient communication has to include avoidance of negative suggestions (16–19) and targeted use of positive waking suggestions (18). In this context, communication could be improved by applying basic principles of hypnotherapy such as employment of indirect suggestions and the establishment of a trusting doctor–patient relationship (rapport). Three RCTs on invasive radiological procedures found that positive suggestions and empathy, with and without techniques of self-hypnosis, were superior to the standard treatment in reducing pain and anxiety and in decreasing consumption of analgesics (20–22). In two RCTs, neutral or positive instructions before blood sampling (“I'm going to start taking the blood sample now”) or induction of local anesthesia led to lower levels of pain than (unintended) negative suggestions (“this may hurt a bit”) (23, 24). A RCT in a hospital emergency room found that the pain-relieving effect of intramuscular diclofenac was not reinforced by a waking suggestion (“this is a powerful painkiller”) in patients with acute headache (25) (eTable 3). Therapeutic waking suggestions can be used by all physicians in a medical context (see Table 3 for examples).

Table 3

Examples of positive waking suggestions at premedication and before induction of anesthesia (modified from [18, 19])

Hypnosis techniques have long been used—and their efficacy assessed—in somatic medicine. The modern evidence-based indications (emotional stress associated with medical interventions, functional disorders such as irritable bowel syndrome) correspond with the applications of mesmerism in medicine in the middle of the 19th century (e5). Learning techniques of self-hypnosis empowers patients to participate in their own treatment and grants them independence. Hypnosis techniques such as the building of a trusting relationship with the patient and therapeutic waking suggestions can considerably reinforce the communicative competence of physicians (15).

Conflict of interest statement

Dr. Häuser receives royalties from the sale of CDs on medical hypnosis in irritable bowel syndrome and fibromyalgia syndrome from Hypnos Verlag. He is an instructor for hypnosis of the German Society for Medical Hypnosis and Autogenous Training (Deutsche Gesellschaft für Ärztliche Hypnose und Autogenes Training).

Dr. phil. Dipl.-Psych. Hagl has received honoraria for authorship or co-authorship of yearly reviews of hypnosis research from the Milton H. Erickson Society for Clinical Hypnosis (Milton H. Erickson Gesellschaft für Klinische Hypnose).

Dr. Schmierer has received an honorarium for authorship or co-authorship from Quintessenzverlag (dental hypnosis).

Prof. Hansen is a member of the scientific advisory board of the Milton H. Erickson Society for Clinical Hypnosis (Milton H. Erickson Gesellschaft für klinische Hypnose).

Manuscript submitted on 28 September 2015, revised version accepted on 7 January 2016